Rotor locator

ABSTRACT

A rotor locator and centrifuge body locator includes a pair of locator arms that close about the rotor shaft and an alignment pin to center the rotor shaft. A registration mechanism rotates the rotor shaft and the centrifuge body until it reaches a known home position. A method of consistently registering the centrifuge body includes centering a rotor shaft of the body along a known center line and aligning the body to a home position both before and after centrifugation.

[0001] This application is a divisional of U.S. patent application Ser.No. 09/637,777 filed Aug. 11, 2000 and titled, “ROTOR LOCATOR,” which iscommonly assigned and incorporated herein by reference. The presentinvention relates generally to rotor location, and more specifically torotor location of a floating rotor.

BACKGROUND

[0002] Centrifuges and other equipment for separating particles insuspension operate by spinning tubes or other containers containing thesuspension at high angular rotational speeds. Centrifugation is commonin medical testing, purification of samples, and other such endeavors.The high speeds of revolution in a centrifugation process are typicallyin the range of 2700 revolutions per minute (RPM) and higher. In orderto accomplish such high speeds of revolution, it is necessary to usehigh speed motors and special precision equipment.

[0003] When multiple samples are placed in a centrifuge, each must belabeled carefully, because the high rotational speeds and the sheernumber of rotations that the centrifuge contents undergo makes it verydifficult to stop rotation of the centrifuge bucket exactly where itstarted. Typically, when multiple samples are placed into a centrifuge,each sample is labeled or coded, and placed individually by a technicianor other operator into the centrifuge. After completion of thecentrifuging operation, the samples are typically removed, again by atechnician or other operator, identified by the labeling, and cataloged,stored, or used accordingly.

[0004] Recently, an automated procedure and apparatus allowing forrobotic placement of multiple samples into a centrifuge was disclosed ingreater detail in co-owned U.S. patent application Ser. No. 09/420,965,assigned to the assignee of the present application, which is hereinincorporated by reference in its entirety. Operation of such anapparatus may be controlled by use of a computer-control system such asthose disclosed in co-owned U.S. patent application Ser. Nos. 09/255,146and 09/361,829, which are also herein incorporated by reference in theirentirety. Such procedures and apparatuses place samples intocentrifuging stations or centrifuges for operation of certain separatingprocesses performed by the centrifuges.

[0005] Rotors of typical centrifuges, because of their extremely highspeeds of rotation, typically “float” in an approximate circular patternwhile they rotate. The rotation is driven by a belt drive connected to amotor off to the side of the centrifuge bucket. The rotor shaft operatesthrough the use of a special bearing assembly which allows the rotorshaft to float, which in turn allows for out of balance rotation, orunbalanced loads in the centrifuge bucket. In other words, the axis ofrotation of the rotor shaft is not closely constrained. When thecentrifuge rotation is slowing down and eventually stops, there isgenerally no reliable method for determining without visual confirmationthe angular position of the bucket. Therefore, samples placed in thecentrifuge are difficult to remove with an automated process, withoutfurther analysis of the samples, such as reading bar codes or the like.

[0006] When using an automated process for placing samples in acentrifuge bucket, and an automated process for removing the sampleswhen centrifugation is complete, it would be desirable to allow forremoval of the samples in the order in which they were placed in thecentrifuge, or in reverse order. It would also be desirable to be ableto remove samples without the need for supervision by a technician oroperator of the equipment.

[0007] Further, when samples are placed in a centrifuge bucket, they maybe placed in such a position that the centrifuge bucket is unbalanced,and rocks off its gravitational center. In such a situation, anautomated process for removing samples, which need to be precise forcorrect operation, may have difficulty aligning with the centrifugebucket after a centrifugation operation.

SUMMARY

[0008] The present invention overcomes the problems of the prior art byproviding in various embodiments methods and apparatuses for location ofthe rotor of a centrifuge, for accurately determining the rotationalposition of a centrifuge bucket, and for aligning a centrifuge bucket toaid an automated process for removal of samples from the centrifugebucket.

[0009] In one embodiment, a rotor locator for a centrifuge includesfirst and second locator arms each having a notch. The notches alignwhen the locator arms move between a first position in which the armsare separated, and a second position in which the arms are substantiallyaligned along one edge. The notches form around a locator pin when therotator arms move to their second position.

[0010] In another embodiment, a centrifuge includes a rotatablecentrifuge body with a number of centrifuge buckets and a cover, a drivemotor coupled to a rotor shaft to rotate the centrifuge body, and arotor locator to move the centrifuge body to a known position.

[0011] In yet another embodiment, a method for locating a centrifugebody includes centering a rotor shaft of the body along a known centerline, aligning the body to a home position, and placing samples in oneor more centrifuge buckets. Once the samples have been placed, they arecentrifuged. When centrifuging is completed, the method further includesre-centering the rotor shaft along the known center line, re-aligningthe centrifuge body to its known home position, and removing thesamples.

[0012] Other embodiments are described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a top view of a rotor locator according to oneembodiment of the present invention;

[0014]FIG. 1a is a view of the embodiment of FIG. 1 taken along lines 1a-1 a thereof;

[0015]FIG. 1b is a view of the embodiment of FIG. 1a with the rotorlocator in a locating position;

[0016]FIG. 2 is a top view of an embodiment of a bucket stop accordingto one embodiment of the present invention;

[0017]FIG. 3 is a side view of a bucket embodiment of the presentinvention;

[0018]FIG. 3a is a cutaway view taken along lines 3 a-3 a of FIG. 3; and

[0019]FIG. 4 is a flow chart diagram of a method embodiment of thepresent invention.

DETAILED DESCRIPTION

[0020] In the following detailed description of the embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural or logical changes may bemade without departing from the scope of the present invention.

[0021]FIG. 1 is a top view of an embodiment 100 of a centrifuge rotorlocator. The centrifuge rotor locator 100 is positioned on centrifuge102 to allow the rotor locator 100 to center the rotor shaft 104 beforeor after a centrifugation process. As has been described above, thecentrifuge rotor shaft 104 typically floats, that is it is notconstrained to a certain axis of rotation. Instead, the rotor shaft isfree to float, maintaining the extremely high revolutions of thecentrifuge without placing undue strain on the rotor shaft 104.

[0022] The centrifuge rotor locator 100 in one embodiment includes apair of locator arms 106 and 108 which are mounted to a cover 110 of thecentrifuge 100. Each of the locator arms 106 and 108 is mounted so as tobe movable from a first centrifuge operating position where the arms areseparated and a second locating position where the arms are together.Locator arm 106 has in one embodiment a pair of notches 116 and 118positioned along one edge 120 thereof. Locator arm 108 has in oneembodiment a pair of notches 122 and 124 positioned along one edge 126thereof. In this embodiment, the edges 120 and 126 are aligned so thatthey face one another, and when the locator arms 106 and 108 rotateabout their respective pivot points, 112 and 114, toward each other, theedges 120 and 126 meet, creating two openings. The first opening in oneembodiment is a substantially circular opening which is comprised of thetwo substantially half circle notches 116 and 122.

[0023] In one embodiment, the locator arms are each movable between thefirst and the second positions by rotation about first and second pivotpoints, pivot point 112 for locator arm 106, and pivot point 114 forlocator arm 108.

[0024] The second opening in one embodiment is also a substantiallycircular opening formed of a combination of notches 118 and 124. Thenotches 116 and 122 form the first opening to locate the rotor shaft 104by confining its position to within the first opening. In thisembodiment, shaft 104 has affixed or attached thereto a rotor shaftbearing 105 which has an outside diameter greater than the rotor shaft,and the notches 116 and 122 close about the bearing, therebyconstraining not only the bearing 105 but also the rotor shaft 104. Thenotches 116 and 122 in this embodiment form an opening substantially thesize of the bearing 105 to constrain the bearing 105 and rotor shaft 104to a known position when the locator arms close to their locatingposition.

[0025] In this embodiment, the notches 118 and 124 contact pin 128 whichis positioned so as to register the position of the rotor shaft 104 asit is confined into position to allow location of the rotor shaft: Thepin 128 and the rotor shaft 104 are positioned in one embodiment inalignment so that the rotor shaft is centered when the locator arms 106and 108 close about the pin 128.

[0026] At the same time the locator arms close about the pin 128, thenotches 116 and 122 close about the shaft bearing 105. Once the locatorarms 106 and 108 close about the shaft bearing 105 and the pin 128, therotating portion 111 of the centrifuge body is registered and located byusing a registration mechanism to ensure that the position of thecentrifuge body is known to a high degree of certainty. When theposition of the centrifuge body 111 is known, the position of theindividual sample holders or buckets 113 in the centrifuge body are alsoknown.

[0027] In this embodiment, the notches 116 and 122 and the bearing 105are sized so as to allow the cover of the centrifuge clearance to beopened without obstruction. The larger openings allowed by the use ofthe bearing 105 allow the cover of the centrifuge to be opened and stillclear the rotor locator mechanism of the present invention.

[0028] In another embodiment, bearing 105 surrounding rotor shaft 104 isnot present, and the notches 116 and 122 of locator arms 106 and 108close instead about the rotor shaft 104 itself.

[0029] In another embodiment, the registration mechanism comprises aregistration disk 130 fixedly attached to the rotor shaft 104. Theregistration disk 130 therefore rotates with the rotor shaft 104. Theregistration disk in one embodiment has a notch or slot 132 cut orformed therein radially inward from the circumferential edge 133 of thedisk 130 toward the rotor shaft 104. An optocoupler 134 having atransmitter 136 and a receiver 138 is positioned so that the transmitter136 and the receiver 138 are located on either side of the registrationdisk 130, as is best shown in FIG. 1a.

[0030] The transmitter emits a light signal. When the disk 130 isbetween the transmitter 136 and the receiver 138, the light signal isblocked by the disk and is not received at the receiver. When the slot132 is interposed between the transmitter and the receiver, the receiverreceives the light signal from the transmitter. The receipt of the lightsignal indicates to logic in an attached motor 140 that controls motionof a gear or other movement mechanism (FIGS. 1a and 1 b) designed toaccurately rotate the rotor shaft 104. The notch or slot 132 in theregistration disk 130 is aligned such that the notch is identified witha home position of the centrifuge body 111. When the notch is positionedso as to allow light to be received by the receiver 138, the logic ofthe motor 140 and the software determine that the disk 130 is in itshome position. Because the disk 130 is fixedly attached to the rotorshaft 104, the location and position of the centrifuge body 111 andbuckets 113 are known with precision.

[0031] A center line of the rotor shaft is established in order toguarantee a predictable and smooth rotation to register the rotor shaftand therefore the centrifuge, even if the load in the centrifuge body isunbalanced or becomes unbalanced during rotation. When the centrifugebody is not spinning, then the rotor shaft is located so that it iscentered on a known center line by closing the locator arms 106 and 108from their first, centrifuge operating position to their second,locating position. The known center line is chosen in one embodiment ofthe invention to be in a position so that the rotor shaft 104, whencentered on the chosen center line, is aligned so that the centrifugebody 111 is in a certain known rotational position. This known positionis in one embodiment a “home” position for the centrifuge body, which inone embodiment is approximately centered in the centrifuge body. Inanother embodiment, the center line is chosen so as to align the rotorshaft, the pin 128, the centrifuge body in the home position, and amachine for automated loading and unloading of samples. In anotherembodiment, pins 129 are positioned so as to limit the travel of thelocator arms 106 and 108 when the arms move to the first position.

[0032] While a home position in which the rotor shaft is approximatelycentered in the centrifuge body 111 provides easy registration of therotor shaft and therefore the bucket, it should be understood that the“home” position for the rotor shaft and therefore the body may bedifferent in different embodiments without departing from the scope ofthe invention.

[0033] Referring now also to FIGS. 1a and 1 b, one embodiment of a rotorlocator 100 is shown in its first, centrifuge operating position (FIG.1a) and its second locating position (FIG. 1b). In this embodiment,optocoupler 134 is positioned on locator arm 106, and motor 140 ispositioned on locator arm 108, so that optocoupler 134 and motor 140move when the locator arms 106 and 108, respectively, move. Motor 140 iscoupled to motor shaft 142 which is driven by operation of the motor.Shaft 142 is coupled to motor gear 144, and rotates motor gear 144 whenit rotates. Rotor shaft 104 has a rotor gear 146 affixed thereto, sothat the rotor gear 146 rotates exactly with the shaft 104. The gears144 and 146 mesh when the rotor locator is in its locating position, androtation of the motor shaft 142 translates into rotation of rotor gear146, which in turn rotates the centrifuge body. The gear ratio betweenthe motor gear 144 and the rotor gear 146 is known, so that rotations ofthe motor shaft have a known rotational effect on the centrifuge body.

[0034] In operation, the locator arms 106 and 108, normally in theirfirst, centrifuge operating position, are moved to their second,locating position. Movement of the locator arms in one embodiment isaccomplished using a piston having a known travel, the piston attachedat one end to locator arm 106 and at the other to a piston housingattached to locator arm 108. Retraction of the piston into the housingdraws the locator arms together. Extension of the piston moves thelocator arms apart. It should be understood that the mechanism by whichthe locator arms are moved may be accomplished in many different ways.It is sufficient that the mechanism is capable of drawing the armstogether and moving them apart. Examples of other arm moving mechanisminclude, by way of example only and not by way of limitation, gears,pistons, hydraulics, electronic solenoids, springs, and the like.

[0035] When the locator arms 106 and 108 rotate to their second locatingpositions, the arm notches 118 and 124 center the arms around pin 128.At the same time, the notches 116 and 122 close about the shaft bearing105, moving it to its known center position. Also at this time, themovement of the locator arms 106 and 108 also move the optocoupler 134into position so that the transmitter 136 and the receiver 138 are in aposition in which the registration disk 130 blocks transmission of lightbetween the transmitter and the receiver unless the notch 132 is betweenthe transmitter and the receiver. Additionally at this time, the motorgear 144 is brought into engagement with the rotor gear 146.

[0036] The location and placement of pin 128 is chosen to make certainthat the body 111 of the centrifuge is properly centered along a centerline, as described above, so that the position of the centrifuge buckets113 can be accurately and precisely determined and effected. Once therotor shaft is centered, then the registration disc attached to therotor shaft is used in conjunction with motor 140, motor shaft 142,motor gear 144, and rotor gear 146 to drive the rotor shaft 104. As longas the receiver 138 does not receive a light signal from the transmitter136, the main centrifuge body is not in its home position.

[0037] When the receiver receives light from the transmitter, thecentrifuge body 111 is in its home position. The home position is usedin conjunction with an automated machine for introducing and removingsamples as described above. Before samples are loaded, the centrifugebody 111 is moved to its home position and the exact location of thebuckets 113 of the centrifuge are known. Samples are placed by theautomated machine into the centrifuge buckets 113 within the centrifugebody 111 in known order, with the body being rotated by the motor 140,which is controlled by software as described above. Once all samples areloaded into the centrifuge, the rotor locator moves to its first,centrifuge operating position. Normal operation of the centrifuge forwhatever purpose is desired is then performed. When spinning of thecentrifuge has completed, and samples are to be removed from thecentrifuge, the rotor locator is moved to its second, locating position,and the method described above is performed to once again move thecentrifuge body to its home position, where the first samples placedinto the centrifuge are positioned exactly where they were when thecentrifuge was loaded.

[0038]FIG. 2 shows a centrifuge bucket stop 200 according to anotherembodiment of the present invention. Each of the centrifuge buckets 113are freely rotatable about a post 202 which is connected to a bracketmember 204. Each bracket member 204 is in turn mounted to the centrifugebody 111. When the centrifuge body 111 rotates, the buckets 113 are freeto also rotate about their respective posts 202. Each of the centrifugebuckets 113 has a number of holders 115 which hold sample tubes.

[0039] Since the centrifuge, its body, and its buckets are finelycalibrated precision machinery, if sample tubes are even slightly off inweight from each other, an unbalancing of the bucket 113 may occur. Innormal centrifuge operation, this is not a problem, as centrifugemanufacturers have designed centrifuges to be operable with unbalancedloads. However, since the buckets are free to rotate, when thecentrifuge is used in conjunction with an automated sample loading andunloading machine as has been described above, an unbalanced load in abucket which causes the bucket to tip can skew the bucket enough todecrease the capability of the automated machine to remove the samplesfrom the bucket. Further, since centrifuge bodies, buckets, rotors, andmoving parts are all precision made to withstand extremely highrotational speeds, it is unwise to tamper with centrifuge parts in thebucket.

[0040] The bucket stop 200 comprises a bucket stop bracket 206 and abucket stop pin 208. The stop pin 208 is in one embodiment press fitinto an opening in the stop bracket 206. The stop bracket 206 is mountedto the bracket member 204 of centrifuge bucket 111 is attached in oneembodiment with existing holes and materials of the bracket member 204.In this embodiment, the stop bracket is screwed or bolted to the bracketmember using an existing opening and screw or bolt of the bracketmember, so as to not place any additional strain or fatigue on thebracket member. The stop pin 208 is positioned so as to limit therotational travel of the buckets 113 located on either side of therespective stop bracket 206.

[0041] In this embodiment, the buckets 113 are restricted from rotationwhich would cause the holders 115 to face away from the rotor shaft 104during rotation, or in other words, the buckets 113 are restricted fromrotation which would be opposite of the expected rotation of the bucketsduring normal centrifuge operation. By limiting the travel of thebuckets 113, the automated machine for removing samples is able tolocate exactly the samples once the centrifuge body 111 and thereforethe buckets 113 are in the home position. Instead, the stop pin 208keeps the buckets 113 at the proper angle and orientation so that therobotics and automated procedures can locate and work with thecentrifuge bucket and registration procedures.

[0042] In another embodiment, each bucket includes an alignment postmechanism 250 comprising a post mechanism base 252 and an alignment post254. The alignment post mechanism is positioned in a known location onthe centrifuge bucket 113. That known position corresponds to the knownposition of an opening in another portion of the mechanism that fits thealignment post 254.

[0043] In one embodiment, the alignment post is positioned in the centerof each centrifuge bucket. In an automated sample loading and unloadingmachine as has been described above, a center screw opening is presentin the loader head. This opening is aligned in this embodiment with thecenter screw opening of the loader head. In this embodiment, noadditional openings are needed in the loader head, as the alignment postmechanism 250 takes advantage of the opening for the center screwalready present in the loader head. In another embodiment, the alignmentpost is tapered, with the largest diameter of the alignment post beingwhere it is attached to the mechanism base 252, tapering to its smallestdiameter at the end 256 distal to the mechanism base 252.

[0044] In another embodiment, each alignment post has thereon a taperedmating piece formed from rubber or another flexible material such as apolymer, plastic, or the like. The taper of the mating piece in thisembodiment or of the post in another embodiment allows a mating openingmore margin for error in initial alignment with the alignment post.

[0045] In other embodiments, the position of the alignment post isdetermined based on post opening position of the automated apparatus.The alignment post mechanism further ensures that the automated loadingof sample tubes will be precise, accurate, and repeatable over manytrials.

[0046] Each of the holders 115 is precision machined in one embodimentfrom a holder plate 210 so that the position of the samples isdeterminable to a high degree of accuracy and precision. In oneembodiment, a molded epoxy bottom piece 300 is placed into each of thebuckets 113, as shown in FIG. 3. This epoxy piece has supports 302, bestshown in FIG. 3a, for supporting the bottoms of the sample tubes toprevent blowing out the tube bottoms during centrifugation. The bottompiece supports 302 also serve to maintain the sample tubes insubstantially the same position they were in when they were placed inthe bucket, also assisting in the removal of the sample tubes by anautomated machine. In one embodiment, the supports 302 are cone shaped.However, it should be understood that the supports 302 are configured tosupport the bottom of whatever type of sample tube is used, and suchmodifications do not depart from the scope of the invention.

[0047]FIG. 4 is a flow chart diagram of a method embodiment 400according to another embodiment of the invention. Method 400 comprisescentering a rotor shaft along a known center line in block 402, aligninga centrifuge rotating body such as body 111 to a home position in block404, and placing samples in one or more centrifuge buckets such asbuckets 113 in block 406. Once samples are placed in the centrifuge bodywhile the body is in its known home position, the samples are subjectedto centrifugation,as desired by the operator, computer system, method orthe like in block 408. When centrifugation is complete, and thecentrifuge body has stopped rotating, the position of the centrifugerotor shaft is again centered along the known center line in block 410,and the centrifuge body is aligned to its known home position in block412. Once the centrifuge body is aligned in its known home position, thesamples are removed in block 414. The operation and process flow ofblocks 402, 404, 410, and 412 are described in detail above with respectto the discussion of FIGS. 1, 1a, and 1 b.

[0048] It is to be understood that the above description is intended tobe illustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A bucket stop for a rotatable centrifuge bucket,comprising: a stop bracket; and a stop pin positioned to limit therotation of the centrifuge bucket.
 2. The bucket stop of claim 1,wherein the stop bracket is mounted to a bracket member for thecentrifuge bucket.
 3. The bucket stop of claim 2, wherein the stopbracket is mounted using existing openings and mounting members of thebracket member.